The breeding ecology of the glaucous-winged gull (Larus glaucescens) on Mandarte Island, B.C.

The breeding ecology and the behaviour of the Glaucous-winged Gull (Larus glaucesens) were studied at Mandarte Island, British Columbia, Canada, in the summers of I96I and 1962. Data were obtained on pair-bondage, pair formation, philopatry to nest site, egg-laying, clutch-size, incubation, egg and chick mortality, fledging rate, growth, age at first flight and colony departure, annual adult mortality and longevity. No support was found for: 1. The Fraser Darling Effect that there is a greater synchronisation of breeding at greater densities; 2. Lack's hypothesis that the clutch size of each species of bird has been adapted by natural selection to correspond with the largest number of young for which the parents can, on the average, provide enough food. In the Glaucous-winged Gull the converse of these theories was established for the year.Science, Faculty ofZoology, Department ofGraduat